Neurons and Synapses

• All our brains are made up of around 100 (65) billion neurons, and that's pretty much all we use to think.
• Neurons are connected by synapses, and most neurons have between 1000 and 10,000 synapses.
• The synapse is a gap which neurotransmitters travel across, e.g. NMDA and Calcium.
• Neurons are cells, like red blood cells are cells.
• Modelling cells is hard, including neurons, but one really simple model is an integrator (from Lapicque 1907 or McCullouch and Pitts 1943).
• Each neuron has an activation level. It collects activation from other neurons (via the synapses), integrates that activation, and if it is over a threshold, the neuron fires.
• When a neuron fires, it loses all its activation.
• The activation is spread via the synapses, and the synapses are typically modelled with a weight.
• There can be negative weighted (inhibitory synapses).
• There are more complicated (and accurate) models such as Hodgkin Huxley models.